Old National Savings savings certificate

Hattie627

I've found an old childhood savings certificate, in physical form in a green-covered booklet with holder's certificate bearing my signature in a pocket at the back. The certificate was purchased in 1967 for £1 and bears an old serial number. It would have matured in 1972 with the addition of 5 shillings (25 pence). If I send this by post to NS&I for redemption, the postage will be roughly half the cost of the sum due. Does anyone know if there is any way of redeeming these historic items by completing an online form? I'm registered for online management of more modern savings with NS&I.